| With the deepening researched and developed of MH-Ni battery materials, the spherical nickel hydroxide cathode material is one of the materials first choice for the battery in the future, because of its advantages on higher power and capacity, smaller memory effects, excellent safety, lower cost, and much more environmentally friendly. However, it is still difficult for the spherical nickel hydroxide applied to cathode material battery, because the spherical nickel hydroxide cathode material would own a higher packing density, while a higher capacity. This problem would still be a challenge to the spherical nickel hydroxide cathode material.In this paper, the current conditions and existing problems in the research of MH-Ni battery was analyzed. The spherical nickel hydroxide particles were synthesized by the controlled chemical crystallization method in a continuous stirring tank reactor. The formation, structure, packing density and electrochemical properties of spherical nickel hydroxide were studied by means of thermodynamic analysis, SEM, XRD and electrochemical techniques analysis. The relationship between pH value, reaction time, nickel ions concentration, mole ratio of NH3/Ni and properties of spherical nickel hydroxide were discussed.The results of thermodynamic analysis showed that nickel hydroxide precipitated totally between pH=9.5 and pH=11.5, and attained an equilibrium conditions in the reaction system. In this case, the nickel ions could be completely precipitated as Ni(OH)2 while mixed with NH3·H2O. It was found from SEM analysis that the crystallinity degree of spherical nickel hydroxide was high. The size of particles distributes equably between a few microns and twenty microns or more. And it was found from XRD analysis that crystal cell becomes integrated gradually and crystal structure becomes more ordered ofβ-Ni(OH)2. The pH value of the reaction is the main factor which affects the structure and properties of spherical nickel hydroxide. Within the certain range of pH value, with the increase of pH value, the packing density and grain size of spherical nickel hydroxide increase at first and then decrease. Too high pH value was disadvantage to the saturation, because the packing density decreases when the pH value is enhanced. When nickel hydroxide precipitated totally between pH=10.5 and pH=11.5, it possesses a high packing density, uniform particle size and good distribution spherical degree. The reaction time was advantage to crystallization. With the increase of reaction time, grain size of spherical nickel hydroxide is increasing which distributes from 2 microns to 18 microns, and the crystalline form becomes from fine aggregate to spherical aggregate. Too low or too high nickel ions concentration was disadvantage to the spherical degree and packing density, and the nickel ions concentration was controlled in the range of 0.1～0.12 mol/L. With the increase of mole ratio of NH3/N1, the packing density of spherical nickel hydroxide increases firstly and then decreases. The mole ratio of NH3/Ni was controlled in the range of 1 to 1.2.Constant current charge-discharge tests showed that the electrochemical properties of the spherical nickel hydroxide electrode characterized with discharge capacity is generally lowered by increasing the size of crystallites and the packing density of the spherical nickel hydroxide particles. The spherical nickel hydroxide possessed a higher discharge capacity and platform potential when it has been precipitated between pH=10.5 and pH=11.5, while the nickel ions concentration was controlled in the range of 0.1-0.12 mol/L, mole ratio of NH3/Ni was from 1 to 1.2, and the reaction time is more than 24 hours.The results showed that the spherical nickel hydroxide with good flowability, high packing density and capacity was prepared when pH=11, the nickel ions concentration was controlled in 0.12mol/L, mole ratio of NH3/Ni is 1.2, and the reaction time is more than 24 hours. |
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